Method of preparing monopersulfate composition containing the triple salt khso4?k2so4?2khso5



June 26, 1962 A. A. D'ADDn-:co ETAL 3,041,139

METHOD OF' PREPARING MONOPERSULF'ATE COMPOSITION CONTAINING THE TRIPLE SALT KHSOH'KZSOH'ZKHSOS Filed `June 24, 1960 7 Sheets-Sheet 2 O IO ZO 50 40 50 6,0 70 O Time hq Days DQURE 2 INVENTORS A\Fred A. D'Addeco DOnOJd .E I QKe. BY Si'ephen E` S-ephomou AGENT June 26, 1962 A. A. D'ADDn-:co ETAL 3,041,139

METHOD OF' PREPARING MONOPERSULFATE COMPOSITION CONTAINING THE TRIPLE SALT KHSOHKaSOH' ZKHSO5 Filed June 24, 1960 7 Sheets-Sheet 5 Havas 3 X- RAY Pow/Daw. DufFRAcnoN PATTERN OF TRIPLE SAL-r KH 501V K25O4ZKH5Q5 Fna-,URE 4 ,m d A www e neen K RAY PQwoaR Donau b. Luke,

AGENT June 26., 1962 A. A. D'ADDlEco ETAL 3,041,139

METHOD oF PREPARING MoNoPERsULFATE COMPOSITION coNTAINING THE TRIPLE SALT KHSOHIKZSOLZKHSO!5 Filed June 24, 1960 7 Sheets-Sheet 4 /MWWWW a MAA/vw w A o AMBA/mk (Moe. Perceni) AGNT' June 26, 1962 A. A. DADDlEco ETAL 3,041,139

METHOD OF PREPARINO MONOPERSULFATE COMPOSITION OONTAINING THE TRIPLE SALT KHSOLIKZSOHZKHSO5 Filedr June 24, 1960 7 Sheets-Sheet 5 KHsos FquRr G @m/15ML AGENT June 26, 1962 A. A. D'ADDlEco ETAL 3,041,139

METHOD OF PREPARING MONOPERSULFATE COMPOSITION CONTAINING THE TRIPLE SALT KHSOH'K2SOH'2KHSO Filed June 24, 1960 57 sheets-sheet e H2504 so ao 7o @o 5o 4o 3o zo lo Kzo..r

GQRE .7

5Q\ \D PHASE RELATxoNS \N SYSTEM KHSOVHLSOA-KZSOA-HLO 45C (M\e Perceh D June 26, 1962 A. A. D'ADDn-:co ETAL 3,041,139

METHOD oF PREPARING MoNoPERsULFATE COMPOSITION coNTAINING THE TRIPLE SALT KHsoH-Kzsoq'zmso Filed June 24, 1960 57 sheets-sheet 7 I TRIPLE SALT Hz 504 @o 2504 MII/MAA V\N\W^ MAMAMAMM H504 ao 2504 17m-.URE

.F d MMIII-c EFFECT OF TEMPERATuRE. ord E: Loket (Mole 'Perceni' AGENT ttes s 041 iss MErHoD or PRaro MoNoransUrrarn CoMPosIrroN coNTArNrNG Tim TRIPLE SALT KHS04 :[{gsogt Alfred A. DAddiec'o Grand Island, N.Y., Donald B.l

This application is a continuation-in-part of our copendng applications Serial No. 549,629, tiled November 29, 1955 and Serial No. 707,034, liled January 3, 1958, which applications are now abandoned. Said application Serial No. 707,034 is a continuation-impart of said application Serial No. 549,629 which in turn is a continuation-in-part of our application Serial No. 525,628, filed August 1, 1955 and now abandoned.

This application relates to monopersulfate compositions and more particularly to potassium monopersulfate compositions, including a new compound which is a triple salt containing potassium monopersulfate, and to their preparation.

Alkali and alkaline earth metal monopersulfates are active `oxygen-containing compounds useful for bleaching and other purposes. Potassium monopersulfate can be prepared readily by a reaction involving monopersulfuric acid and the hydroxide, carbonate or bicarbonate of potassium. However, as generally prepared by methods described in published literature, potassium monopersulfate compositions are relatively unstable and hygroscopic.

Active oxygen may be deiined asv the -oxygen in the monopersulfate molecule in excess' of that required to form the corresponding bisulfate. It may be calculated as a percentage from the equation for the decomposition of the monopersulfate,

Percent A O.- Wt' of [O] "WF of xnso. 100

where A.O.r represents the active oxygen and [O] is the oxygen liberated by the decomposition shown. In applying ile formula given, the weight of KHSO5 is replaced by the Weight of sample where impure material is used. Active oxygen can, of course, be determined from. many v reactions, the displacement of iodine from potassium is a triple salt of potassium monopersulfate, potassiumA bisulfate and potassium sulfate. Y

A further object is -to provide solid potassium monopersulfate compositions containing the above new compound, and a method for their production.

Still further objects will be apparent fromthe following description. v

The products of the invention are the new triple salt 3,04l,l39 Patented June 26, 1962 2 compound of the formula KHSO4-K2SO4-2KHSO5, and solid compositions containing said triple salt in admixture with one or more of the single salts KHSO5, KHSO4 and K2SO4 and/ or with one or more double salts whose components are two of said single salts, in such proportions as are indicated below. The process of the invention involves forming an aqueous solution having a solute compositionas defined hereinafter and recovering a solid product containing said triple salt om the solution.

FIGURE 1 of the accompanying drawings is a ternary diagram in which the area of the closed curve ABCJD represents the solid compositions of the invention.

FIGURE 2 is a diagram showing7 typical decomposition curves for the potassium monopersulfate compositions.

FIGURE 3 is a reproduction of the X-ray powder diffraction pattern of the new triple salt compound.

FIGURE 4 is a reproduction of the X-ray powder diffraction pattern of pure potassium m-onopersulfate, KHS`O5.

FIGURES 5, 6 and 7 are phase relations diagrams for the system KHSO-HZSOg--KZSO4--H2O` at temperatures of 15 C., 30 C., and 45 C., respectively.

FIGURE 8 is acomposite of the diagrams of FIGURES 5, 6 and 7 and shows the eiects of temperature on the triple salt field in the above system.

The compositions of the invention are characterized by having present therein a substantial proportion, i.e., at least 5% and preferably at least 50% by weight, of the triple salt, KHSO4-K2SO4-2KHSO5. The compositions will in general have the over-all chemical compositions, in terms of the single component salts (KHSO4y KZSO.,E and KHSOs), represented by the area within the closed curve ABCID of yFIGURE l. Since those compositions represented by the area Within the closed curve AUD are distinguished from the other compositions of area ABC] D by being much less hygroscopic, they constitute preferred compositions. Of such preferred compositions, those having a triple salt content of at least 50% by weight are most preferred.

The triple salt contents of the compositions of the invention will generally be about equal to the maximum contents which are theoretically possible, based upon the actual contents of the component single salts. Actual triple salt contents can be determined approximately by X-ray diffraction methods.

The compositions of the invention l'can be prepared from readily accessible materials such as oleum, hydrogen peroxide and potassium hydroxide, carbonate or bicarbonnate. Conveniently, oleum containing 5 3 to 82% dissolved SO3 based upon the total Weight of theoleurn, is reacted with aqueous hydrogen peroxide containing 35 to 90% H2O2 by weight in the proportion of from 1 to 1.8 moles of oleum (dissolved plus combined $01,) per mole of H2O2 to give a mixture of monopersulfuric and sulfuric acids, which mixture is then reacted with sufficient potassium hydroxide, carbonate or bicarbonate to give a second mixture having a pH of about 1.5-2.5, preferably 2.0-2.5. As is disclosed in Stephanou application Serial No. 476,607, tiled December 20, 1954 and issued August 13, 1957 as Patent 2,802,722, the proportioning of the reactants so as to give a mixture having a pH greater than 3 should be avoided, otherwise decomposition with loss of active Ioxygen becomes excessive.

In practicing the invention by reacting la mixture of monopersulfuric and sulfuric acids with potassium hydroxide, carbonate or bicarbonate, the reactants may be so proportioned as to give a reaction mixture having a solute composition (in terms `of KHSO5, KHSO., and K2SO4) represented by a point within the area of the closed curve ABC] D of FIGURE l, and then recovering product from the mixture, e.g., by evaporating to dryness or by crystallization procedures. The resulting product ..2 will be substantially more stable than are the compositions represented by those areas of FIGURE 1 designated as unstable The single salts, KHSO5, KHSO4 and K2SO4, can themselves be employed by forming aqueous mixtures thereof in proper proportions to give aqueous systems from which the products of the invention can be recovered. Alternatively, eitherpotassium sulfate or bisulfate can be added as a solid or in separate solution during the reaction of monopersulfuric acid land potassium hydroxide or carbonate to form a mixture of the required composition from which the desired product is recovered.

The pure triple salt, KHSO4K2SO4-2KHSO5, if desired, can be readily obtained by fractional crystallization procedures. The solute compositions of solutions which will give the triple salt upon being concentrated to crystalline a solid product therefrom are readily apparent from FIGURES 5, 6 Iand 7.

The phase relations at l5 C., 30 C., and 45 C. for lthe system KHSO5-H2SO4-K2SO4-H2O `are shown partially in FIGURES 5, 6 and 7, respectively. Each triangular diagram of these ligures represents the base `of a right prism in which 'the height (not indicated) represents the concentration of water. In each figure, the triple salt `area or field ABCDE represents the solute compositions of all solutions in equilibrium with solid triple salt. Similarly, the K2SO4 field represents the solute compositions of solutions in equilibrium with solid K2SO4 while the boundary between those two fields represents the solute compositions of solutions in equilibrium with both solid triple salt and solid K2SO4.

Details of the phase relations for the bottom portion and for the left side of the diagrams of FIGURES 5, 6 and 7 have not been completely established, However, as to the bottom portion the indications are that the prevalent solid phases Iare KHSO4, K2SO4 and Vanious H2SO4K2SO4 complexes, and that boundary line CD represents the solute compositions of solutions in equilibrium with the triple salt and one such complex, as shown in the figures. Thus, at 30 C. definite indications were obtained that .the the complex in equilibrium with the triple salt and solution at boundary CD is 3 H2804 4K2SO4 this complex is also shown for the sake of simplicity in the other figures. Also, there are strong indications that when solutions with solute compositions of about 50-7S% KHSO5, 9-26% H2SO41and 12j-24% K2SO4 (mole percent) are evaporated to dryness at temperatures under about 60 C. Kthere are obtained solid products containing a complex of KHSO5 and KHSO4, which complex is probably a hydrate of a double salt of the formula KHSO4-2KHSO5. The existence of some such double salt is shown by the fact that some product fractions give an X-ray powder diffraction pattern distinctly different from the patterns for KHSO5, KHSO4, K2SO4 or the previously mentioned triple salt. Such a double salt has not been isolated in pure form, and its existence has not been indicated on the diagrams of FIGURES 5, 6 and 7. If all details of the upper left side of those diagrams were known, it seems likely that a field for such double salt would occur somewhere in the upper left hand portion of the diagram between the Kil-1805 and the triple salt fields.

Continued drying at Gli-100 C. of a solid product containing the above complex of KHSO5 and KHSO4 converts the complex to another complex of KHSO5 and KHSO4, believed to have the formula KHSO52KHSO4- This latter complex also gives 'a distinctive X-ray powder diiraction pattern. The first of these complexes also converts on standing to the second with loss of active oxygen, and is more hygroscopic than the second. The presence of substantial amounts of the rela-tively unstable first complex may explain why some products `are relatively unstable when first made but become more stable upon standing as indicated by the curves of FIG- URE 2. Since the second of the above complexes is relatively thermally stable at 60-100 C. whereas the first is not, drying at temperatures above 60 C., eg., 60-80 C., or subjecting product dried at a lower temperature to a subsequent heat treatment Iat such higher temperatures, facilitates 1obtainingproduct having ya low rate of active oxygen loss under usual storage conditions. Essentially the same result is achieved if product which is relatively unstable due to the presence of the first of the labove complexes is permitted to stand or age for a time under normal temperature conditions. However, even the above relatively stable second complex (believed to have the formula KHSO5'2KHSO4) in KHSO5-KHSO4--K2SO4l systems converts on long standing to the more stable triple salt, KHSO4 K2SO4 2KIISO5.

It can be seen from FIGURE 8 that temperature has a relatively minor effect upon the right side, a moderate effect upon the bottom and `a fairly pronounced effect upon the left and top sides of the triple salt field. The exact effect upon the -top side is somewhat uncertain at the higher temperature because of the difficulty of obtaining yaccurate analytical data for systems high in KHSO5 at C. due to the high solute concentrations and high viscosities of such systems at that temperature. Some extrapolation .and use of `analogy with data for lower ternperature were therefore necessary to complete the bound aries in the uncertain regions. However, the boundaries of the triple salt field are believed to be substantially as shown in FIGURES 5 through 8.

Ordinarily, phase boundaries are represented by curves. However, the eurvatures of the boundary lines 4for the triple salt field are slight and for practical purposes the boundaries may be represented by straight lines las has been done in FIGURES 5 through 8 which show the triple salt field as an irregular Pentagon with corners A, B, C, D and E. This makes it possible to derive equations giv- 1 ing the shape and size of the triple salt field as a function of temperature. By means of these equations, interpolation and moderate extrapolation are possible.

The locus of any one corner, eg., A, of the pentagon representing the triple salt field as a function of temperature -is given by the equations:

where X, Y and Z, respectively, are concentrations of KHSO5, H2804 yand KZSU.; in mole percent, Tis temperature C.) Iancl all Ks are constants. Thus, the positions of the five corners of the pentagon representing the triple salt field can be calculated for `a given temperature from the following independent equations in which the `numelical values worked out for the constants have been inserted:

Corner A X=97. 62-I-0. 1433 T-O. 00493 T2 Y= 1. 37-0. 0190 T-0. 00002 Tl B X=17. 10+2. 279 T 0. 01373 Tz Y=83. 62-2. 2919 T0. 02702 T C X =31. 08-0. 1907 T+0. 006627 T2 Y=54. 42-0. 3937 T-0. 0018-1 T2 D X =25. 91+0. 4097 T-0. 00402 T2 Y=42. 01-0. 3930 T+0. 00180 Tn E X=89. 30-1. 894'T +0. 03447 T2 TABLE I Corners for Triple Salt Field [Temperatures in C.-Cornpos1tions in Mole Percent] Temperature KHS-O H2304 KzSOi Corner 98. 56 1. 18 25 A 38. 51 57.13 4. 34 B 29.84 50. 30 19. 85 C 30. 20 38. 26 31. 52 D 73. 8l 10. 37 15. 8G E 98. 66 1.08 24 A 48. 19 45; 91 5. 89 B 29. 71 48. 10 22. 17 C 32.05 36. 52 31. 41 D 68. 65 12. 93 1S. 40 E 20 98. 51 98 49 A 57. 18 3G. 04 6. 76 B 29. 92 45. 81 24. 26 C 33. 69 34. 87 31. 42 D 65. 21 14. 58 20. 19 E 25 98.12 88 .9S A 65. 48 27. 53 6. 98 B 30. 45 43. 43 26. 11 C 35.14 33. 31 31. 54 D 63. 50 15.32 21.16 E 97.48 .78 1.72 A 73. 10 20. 36 6. 53 B 31.32 40. 95 27. 71 C 36. 38 31. 84 31.76 D 63. 51 15. 16 21. 32 E 96. 59 .68 2. 71 A 80. 03 14. 55 5. 41 B 32. 52 38. 38 29. O8 C 37.42 30. 46 32.10 D 65. 24 14. 09 20. 65 E 95. 46 .57 3. 95 A 8G. 27 10. 08 3. 63 B 34. 05 35. 72 30.21 C 38. 2G 29. 17 32. 55 D 68. 70 12. 11 19. 17 E 94. 08 47 5. 43 A 91. B3 6. 97 1. 18 B 35. 91 32. 97 3l. 10 C 38. 90 27. 97 33. 11 D 73.88 9. 23 16.88 E

Any solution whose solute composition lies within the triple salt field of FIGURES 5 to 7 will, upon evaporation, yield solid triple salt. Recovery of pure triple salt usually will not be required although solid products containing at least and most preferablyl at least 80% by Weight of the triple salt are definitely advantageous. It is generally preferred to effect crystallization of triple salt product by a continuous operation in which the aqueous phase from which the crystallization is effected has a solute composition corresponding to component values of from 50-78% KHSO5, 9-26% H2804 and 12.5-24% KZSO.; (mole percent). The component values should, of course, be chosen from Within the above ranges so that the solute composition will be within the triple salt field of the phase relations diagram for the temperature at which crystallization is eiected.

Thus, when using aqueous lpotassium,hydroxide (e.g., of about 45% KOH by weight) and a mixture of monopersulfuric and sulfuric acids (containing about 59.1% H2SO5, H2804, H202 and. H2O Weight) as reactants, continuous streams Vthereof are conveniently separately added to and mixed with a stream of reaction slurry which is continuously circulated from a vacuum evaporator (operated at about 25-35 C. and 20-30 mm. Hg absolute pressure) through a steamheated calandria and back to the evaporator. A product slurry stream is continuously removed from the recirculation system, centrifuged, and the mother liquor returnedto the recirculation system. When the reactant streams fed to the system are proportioned so as to maintain the solute composition of the liquid phase of the system at about 74% KHSO5, 12% H2804 and 14% K2SO4 (mole percent) and the wet centrifuge cake is dried in a rotary drier with a countercurrent stream of hot air (6D-80 C.), ,there is obtained a dry product having an over-all composition corresponding to about 50% KHSO5, .25% KHSO4 and 25% K2SO4 V(mole percent).l The productk will contain about 95% or more by Weight of the triple salt, KHSO4K2SO4 2KHSO5, with perhaps small amounts of KHSO5, KHSO4, K2SO4 and/ or various complexes or solid solutions of pairs of the single salts such as the KHSO5-KHSO4 complexes mentioned previously.

Commercial products should exhibit a low rate of active oxygen loss under normal handling and storage conditions. Such rate of active oxygen loss should generally be less than 2%, and preferably will be less than 1%, per month at room temperature (-25 C.). The terms stable products and stable compositions are used herein to mean products and compositions which lose active oxygen at a rate not exceeding 2% per month at room temperature. The `rate ofv active oxygen loss can be determined from the results of analyzing a given product sample at the beginning and end of a one-month storage period at roolntemperature and this method of testing is referred to as the storage stability test.

Manometric determinations of the oxygen evloved through loss of active oxygen in short periods of time at a constant temperature of 25 C. can be used to determine what may be termed instantaneous rates of loss of active oxygen. When using this instantaneous stability test, it is convenient for comparison purposes to calculate the results in terms of the percent of original active oxygen that would be lost in one month at 25 C.

Another convenient test involves heating a dry test sample at 50 C. until its rate of evolving oxygen through loss of active oxygen becomes substantially-constant, as shown by measuring manometrically 'the oxygen evolved, and determining the amount of active oxygen still present in the sample when a constant rate of evolution has been reached. This accelerated dry stability test provides a simple and rapid Way yof determining how much active oxygen can be expected to be lost before a stable product will be obtained. Experience has shown that when the rate offloss of active oxygen becomes constant under the conditions of the test, the sample will generally have reached a stable state where its rate of loss of active oxygen as determined either by the above storage stability test or the instantaneous stability test will not exceed 2%, and generally will ynot exceed 1%, per month at 25 C. Naturally, a product which loses a high proportion of its active oxygen before reaching a stable state is less desirable than one which initially is stable or loses only a small proportion of its active oxygen before arriving at a stable state.

Referring to FIGURE 1, the product compositions represented Iby the area within the closed` curve ABCJD are generally stable in accordance with the above definition. However, as has :been indicated,l previously, when product is recovered by crystallization followed by drying of the crystals wet with mother liquor, there may ibe obtained products which initially are relatively unstable but become stable upon aging or upon being heated. Such initial instability appears to be due largely to the coating of ythe crystals with material containing a relatively unstable complex such as 2KHSO5KHSO4 formed as the mother liquor wetting the .crystals dries.

In general, compositions within the area of the closed curve ABCJD of FIGURE 1 are decidedly more stable than are the compositions of the other areas designated as unstable Furthermore, of the compositions represented by area ABCJD, those of the more restricted area AUD are generally the more stable, probably because they are distinctly less hygroscopie. Line IJ represents approximately the 7% hygroscopicity' curve. Numerous tests haveestablished that, in general, compositions of the diagram below that line have hygroscopicities less than 7% while those above have hygroscopicities greater than 7%. Furthermore, hygroscopicity increases quite abruptly as the compositions move up from line IJ.

The hygroscopicity values reported herein represent the percent increase in weight of a sample resulting from the constant exposure of the initially dry sample at 25 C. to air at 80% relative humidity until no further gain in weight occurs. A few representative hygroscopicity values among the many that have been determined for products of a wide range of compositions are shown in Table II.

TABLE II Hygroscopzczty vs. Product Composztzon Composition, mole percent Hygroscopicity, percent gain in weight at 25 C., KHSOs KHSO4 K280i 80% R.H.

All'of the above compositions are within area ABC] D of FIGURE 1. All with hygroscopicities less than 7%, i.e. the last 5, tall below the 7% hygroscopicity curve IJ, while all with hygroscopicities greater than 7% (the rst 6) fall above curve II.

Probably the best known prior method of preparing a potassium monopersulfate product is that of Price, Journal of the Chemical Society (Trans.) 89, part I (1906), pages 53-8, which appears to be essentially the same as the method described in Mellor, "Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 10 (1930), pages 482-3. Prices method involves adding potassium carbonate to a mixture of monopersulfuric and sulfuric acids and their potassium salts until eiervescence ceases, separating the precipitated K2804, concentrating the resulting neutral solution by evaporation in a vacuum over concentrated H2804 during a 1-2 week period while periodically filtering ol the K2S04 which separates continuously, and then allowing the evaporation to go to'dryness. Price yreported that his products contained KHSOS, KHSO4, K28208 `and K2S04 `and gaveanalytical data for their compositions. 'It is clearly evident from those data Ithat his products were quite different in composition from the present products. Furthermore, we have found that products similar in composition to those of Price are substantially less stable than are those of area ABCJD and they are substantially more hygroscopic than are products of compositions represented by area AIJD of FIGURE 1. i

Products having over-all compositions approximating those reported by Price were prepared by dissolving KHS05, KHSO4 Vand 142804 in water to give concentrated solutions having solute compositions approximating the over-al1 compositions of the desired nal dry products, then freeze-drying the solutions, then further drying the solid product over a desiccant to constant weight. Active oxygen losses were slight so that the proportions of KHSO5, KH804 and K2804 in the final products were essentially the same as in the starting solutions. Some of the products were subjected to the above hygroscopicity test, while the remaining were subjected to the instantaneous stability test. The results were as follows:

draft oven at 50-60 C. for 4 hours.

8 TABLE n1 Properties of Price-Type Compositions Active oxygen loss/ Hygroscomonth percent l Pro- KHSO5 KHSO; KgSO4 picity,

ct percent Initially After heating 1 Determined by instantaneous stability test at 32 C. (Instead of 25 C.) 2 Determined after the sample had been heated for 20 hours at 65 C The invention is illustrated further' by the following examples in which all percentages are by weight unless indicated otherwise.

EXAMPLE 1 This example shows the preparation of an unstable monopersulfate composition.

(A) An acid solution containing 61% H280;J and 23% H2802 was partially neutralized with 50% potassium carbonate solution. The resulting slurry was tray-dried in a forceddraft oven at 50-60" C. and the product analyzed. The product, which initially contained 5.46% active oxygen, analyzed 51.8% KHSO5, 11.0% KHSO.,t and 37.2% K2S04. The mole ratio KHSO5zKHSO4zK2SO4 was 4.2:1:2.6. The composition in mole percentages based on the three component salts was 53.8% KHS05, 12.8% KHSO4 Aand 33.3% K2804 which is outside the area of lthe closed curve ABCID of FIGURE 1.

The dried mixture was allowed to stand at room temperature (about 25 C.) in a vented bottle for several weeks and analyses were repeated at intervals. The active oxygen fell during the first day to 5.1%, a loss of around 6.6%. The active oxygen loss in -a three-week period was about 20%. By the end of three weeks, the loss of active oxygen was very slow and the rate remained practically constant.

(B) An equilibrium mixture, 200 grams, containing 59.3% H2805 (1.04 moles) and 27.4% H2804 (0.559 moles) was neutralized with 50% aqueous potassium carbonate nearly completely to KH805 and K2S04. The slurry was lyophilized by freezing and dehydrating the frozen material under a vacuum of about 0.1-0.3 mm. of mercury. The dry product contained 52.7% KH8O5 (5.55% active oxygen), 6.5% lil-1804, 39.3% K2S04 and 1.5% moisture. The mole ratio KH8O5:KHS04:K2VSO4 was 7.26:1:4.7,3. The composition in mole percentages, based on the three component salts, was 55.9% 141-1805,

7.7% KHS04 and 36.4% K2S04 which is outside theV area of the closed curve ABCJD of FIGURE 1.

When tested by the accelerated dry stability test, the lyophilized product of this example showed an active oxygen loss of 28% before the rate of active oxygen loss became constant.

EXAMPLE 2 This example shows the preparation o-f a stable monopersulfate composition.

In a reaction vessel equipped with a mechanical stirrer was placed 200 g. of a mixture of H2805 and H2804 containing 63.3% H2805 (1.11 moles) and 20.2% H2804 (0.412 mole). To the stirred acid mixture maintained at 5-10 C. by external cooling was added slowly 267.4 g. of 50% aqueous K2C02 (0.967 mole).

The resultant slurry was then tray-dried in a forced- Analysis of the product immediately after drying was as follows: 50.8% KHS05 (5.32% active oxygen), 21.2% KHS04, 27.7% K2SO4 and 0.3% moisture. The mole ratio 'was l2.14:1:1.02. The'composition in mole percentages,

based on the three component salts, was 51.5%l KI-ISO5, 24.0% KHSO4 and 24.5% K2SO4 which is within the area of the closed curve ABCJD of FIGURE 1.

The product was tested by the accelerated dry stability test. lResults showed there was an initial loss of oxygen corresponding to 1% per month, prob-ably while some moisture was still present in the sample. The loss rate rapidly fell to less than l per month and then remained constant.

This example shows the preparation of a preferred composition of the invention.

An attempt was made to prepare a composition having a theoretical KHSO5:KHSO4:K2SO4 mole ratio of 2:1:1 by adding together the required amounts of the solids in water and freeze-drying the slurry. The product obtained had an actual mole ratio of 1.95:1:0.96, and contained 5.22% active oxygen.

The accelerated` dry stabilityjtest applied tothe sample prepared as described showed that the active oxygen loss immediately obtained was less than 1% per month.

EXAMPLE 4 This example shows the preparation of monopersulfate mixtures from substantially pure potassium monopersulfate.

A. Potassium monopersulfate was prepared by reacting a mixture of monopersulfuric acid `and sulfuric acid containing 63% by weight H2805 and about 20% H2804 with an amount of 50% aqueous potassium carbonate equivalent to the monopersuilfuric acid present. The precipitate was collected on a sintered glass funnel by vacuum filtration and Washed with several portions of cold '10 .'(1) The crude product was dissolved in a amount of Water and the solution was cooled until some crystallization occurred. After separating the crystals,

the solution `became faintlyV turbid. The mixture Was cooled and the crystals vwhich formed were separated. To the mother liquor was added more ethanoljand the procedure was repeated until a crystal fraction 'of substantially pure potassium monopersulfate was obtained.

The crystalline products from the above procedures were found to contain 10.44% of active oxygen, within 0.1% of the theoretical value for -KHSO5. This pure product crystallizes as water-white platelets melting at 100 1C. with decomposition. It does not ignite when heated rapidly to high temperature nor detonate when subjected to the `Bureau of Mines impact test. The dry material is hygroscopic. So far as known, no monopersulfate product has heretofore been reported with such a high active oxygen content.

B. -Monopersulfate compositions were made up in solution from the purified material of (.A) by mixing therein varying proportions of potassium bisulfate and potassium sulfate. The resulting solutions were evaporated to dryness and the dried compositions were allowed `to stand at room temperature and tested at intervals for active oxygen content. FIGURE 2. The curves, going from top to bottom of FIGURE 2, are the decomposition curves for samples 10, 22, 25 and 24, respectively of Table -IV below.

Stability and other pertinent data fora number of product samples are given in Table IV.

TAB-LE :IV

Storage Stability (Room Temperature) vs. Product Composition Immediately after sample preparation At stabilization No. Weight percent Mole percent Weight percent Mole percent KHSO5 KHSO; Kgs O4 KHSO5 KHSOl K280i KHSOt KHSO; KzSO, KHSO; KHSO4 K250i 98. 00. 1. 98. 1. 95. 00. 3. v 94. 3. d L w. L 76. 19. 3. 74. 3. 74. 13. 11. 74. 10. 70. 8. 20. 72. 18. 62. 19. 17. 62. 15. '64. 16. 19. 64. 1l t 59. 18. 22. 59. 19. 60. 12. 27. 61. 24. 60. 37. 2. 57. 1. 60. 9. 29. 62. 26.

absolute ethanol. After drying in a vacuum desiccator,v the crude product contained the equivalent of 88.4% KHSO5 (9.31% active-oxygen), 9.6% KI-ISO.,l and 2.0% KZSO.; and-represented an active oxygen yield of 41.5

Pure potassium monopersuliate was obtained lfrom the above crude product by each of the following fractional crystallization procedures:

The compositions of the samples of Table I-V are plotted in FIGURE l in terms of the equivalent contents of the three component salts KHSO5, IQHSO4 and K2SO4. In FIGURE l, lines EAIBF and GCIDH represent the general boundariesbetween` areas `of stable and unstable compositions. Pure potassium monopersulfate, KHSO5 is stable, as indicated in the figure. The products whose Typical decomposition curves are shown in TABLE V Comparison of Physical Properties of the Salts KHSOs KHSO4 K280i KHSO4K2SOr2KHSOs Crystal system Orthorhombic.. Orthorhombic- Orthorhombio. Unit cell dimensions (Angstroms) a. 5.771 a.8.60.

c. 7.518 o. atblc. 0. 8609:1:1.934-.- 0. 5727 :120. 7418 0. B17111787. Molecules/unit cell 4 4 got the triple salt). Crystal density, gms/m1 2. 662 2. i122 2. 13. Hygroscopic (Yes or No) Yes. No No. Stability, percent active oxygen loss/month at 32 C 1% 1% Solubility at C., gms/100 gms. H10- 40 36. 6 6. 85 27.

compositions are represented by the area of the `closed curve ABCJD are also stable and have the distinct advantage over pure potassium monopersulfate of being more readily and economically obtainable by commercially feasible methods. Products containing less than the equivalent of 5 mole percent KHSO5, represented by the area below line AD, are generally too low in active oxygen to be of commercial interest. Thus, the area within the closed curve ABCJD represents the improved solid stable compositions of the invention, including the new triple salt, while the area within the closed curve AIJD represents the preferred compositions.

The relatively small area of the closed curve UK of triple salt by direct precipitation from a reaction mixture.

EXAMPLE 5 A concentrated reaction solution having a solute composition corresponding to S1 mole percent lil-1805, 23 mole percent KZSO.; and 26 mole percent H2504 was crystallized slowly at 0 C. The crystals which formed were found by analyses to correspond to the vformula They gave an X-ray powder diffraction pattern which is distinctly dilerent from the pattern for pure potassium monopersulfate. Unit cell measurements on a single crystal of this triple salt gave crystallographic data distinctly dilerent from those for potassium bisulfate and potassium sulfate. A comparison of the physical properties of the triple salt with those of the single component salts is given in Table V.

The present triple salt has yan X-ray powder diffraction pattern which is distinctly diierent from those for KHSO5, KHSO4 Vand K2SO4. FIGURE 3 is a reproduction of its X-ray powder diffraction pattern obtained by means of a Norelco X-Ray Diffraction Unit using CuK,1 radiation and employing standard techniques. In FIGURE 3, the ordinates 1" represent peak heights and the -abscissas "20 represent the positions of the peaks, where 0 is the Bragg angle. The X-ray powder diiraction pattern of pure potassium monopersulfate, KHSO5, was similarly determined and is reproduced in FIGURE 4.

The d" values, in Angstroms, of the major peaks of the diffraction patterns of FIGURES 3 and 4 are given in Table VI.

TABLE VI d Values in Angstroms, of Major Peaks of Diffraction Patterns of FIGURES 3 and 4 Figure 3 Figure 4 KHSO4KnSO4-2KHSOn KHSOu The triple salt compound whose X-ray powder diiraction pattern is shown in FIGURE 3 generally contains a small amount, about 0.60.7% by weight, of water. This Water, which is tenaciously retained, corresponds roughly to one molecule per unit cell (4 molecules) of the triple salt. lf it is present 4as water of hydration, which seems likely, the compound formula may be represented as (KHSOa-KgSOyZKHSOLfHZO for'which the calculated water content is 0.7 3%. However, if the triple salt is crystallized from aqueous solution at low temperatures,

e.g. 0-l0 C., fit does so as a higher hydrate having an X-ray powder diiraction pattern different from that of FIGURE 3. This higher hydrate loses water of hydration readily at room temperature or on washing with methanol to yield the compound whose X-ray powder diiraction pattern is that of FIGURE 3.

Itis clear from a comparison of the diffraction patterns of FIGURES 3 and 4, from the d values of Table VI, and from the properties of Table V that the triple salt is a new and distinct chemical compound. It is stable lin the solid state, is non-hygroscopic and is useful as an oxidizing agent, e.g. for fbleaohing various materials. Other solid products, represented by the area within closed curve ABCJD of FIGURE 1, which products contain substantial -amounts of the triple salt are also stable and similarly useful.

'Ilhe embodiments of the invention in which an exclu- 1sive property or privilege is claimed are deined as folows:

1. The triple salt compound, KHSO4K2SO4`2KHSO5 13 vl2. A solid composition containing to about 95 by weight of the triple salt compound,

and having, in terms of KHSO4, K2SO4 and KHSO5, an over-all composition represented by a pointvwithin the closed curve ABCJD of FIGURE 1.

3. A solid composition containing 50 to about 95% by weight of the triple salt compound,

and having, in terms of KHSO4, KZSO., and KHSO5, `an over-all composition represented by a point Within the closed curve ABCID of FIGURE 1.

4. A solid composition containing 5 to about 95% by weight of the triple salt compound,

and having, in terms of KHSO4, K2SO4 and KHSO5, 'an over-al1 composition represented by a point the closed curve AIJD of FIGURE 1.

5. A solid composition containing 50 to about 95 by weight of the triple salt compound,

and having, yin terms of KHSO4, KZSO.,F and KHSO5, an over-all composition represented by a point within the closed curve AUD of FIGURE 1.

6. A solid composition containing 80 to about 95 by weight of the triple salt compound,

and having, in terms of KHSO4, K2SO4 and KHSO5, an over-all composition represented by a point within the closed curve AIJ D of FIGURE 1.

7. The method comprising forming an aqueous solution at =a temperature within the range to 45 C., which solution has a solute composition represented by a point within the triple salt (KHSO4-K2SO4-2KHSO5) ield ofthe phase diagram at said temperature for the system KHSO5-H2SO4-K2SO4--H2Q and crystallizing the triple salt, KHSO4-K2SO42KHSO5, from said solution at said temperature, said triple salt field having the shape of an irregular pentagon whose corners A, B, C, D

14 and E, respectively, have the positions on said phase diagram defined by the following equations:

Corner A X 97. 624-0. 1433 T-O. 00493 T2 Y= 1. 37 -0. 0190 T-0. 00002 Tz 5 B X 17. 10+2. 279 T 0. 01373 Tz Y=83. 62-2. 2919 T-0. 02702 T2 C X =31. 08-0. 1907 T-I-O. 006627 Tz Y=54. 42-0. 3937 T-0. 001847"2 D X =25. 91-1-0. 4697 T0. 00402 Tz Y=42. 01-0. 3930 T+0.'00180 Tz E X=S9.301.894T +0. 03447 T2 Y= 2. 54+0.9647 T0. 01813 Ts in which equations X and Y, respectively, are the concentrations in mole percent of KHSO5 and H2504 and T is said temperature.

8. The method of claim 7 wherein the crystallized triple 15 salt is separated from mother liquor and the separated salt wet with mother liquor is dried.

9. The method of claim 8 wherein drying is eiected 'at a temperature of 60 to 100 C.

10. The method comprising forming an aqueous solution at a temperature within the range of 10 to 45 C.,

9 to 26% HZSO.,l and 12.5 to 24% K2SO4, and crystallizing the triple salt, KHSO4-K2SO42KHSO5, from said solution lat -said temperature.

11. The method of claim 10 wherein the temperature is within the range 25 to I35 C.

5 12. The method of claim 11 wherein the triple salt is separated from mother liquor and the separated salt wet with mother liquor is dried.

13. The method of claim 12 wherein drying is effected at a temperature of from 60 to 100 C.

Stephanou Aug. 13, 1957 Lake et al. May 12, 1959 UNITED STATES PATENT OFFICE CERTIFICATEV OF CORRECTION Patent No 3,041,139 June 26, 1962 Alfred A. D'Addieco et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columns 9 and lO TABLE IV column 9 l' "1803" read 19.3 in lne 22 thereof, for

Sigo-ed and sealed this 16th day of October 1962.

(SEAL) Attest:

ERNEST w. swlDI-:R DAVID L LADD Attesting Officer Commissioner of Patents 

7. THE METHOD COMPRISING FORMING AN AQUEOUS SOLUTION AT A A TEMMPERATURE WITHIN THE RANGE 10 TO 45* C., WHICH SOLUTION HAS A SOLUTE COMPOSITION REPRESENTED BY A POINT WITHIN THE TRIPLE SALT (KHSO4.K2SO4.2KHSO5) FIELD OF THE PHASE DISGRAM AT SAIDD TEMPERATURE FOR THE SYSTEM KHSO5-H2SO4-K2SO4-H2O5, AND CRYSTALLIZING THE TRIPLE SALT,KHSO4 K2SO4 2KHSO5, FROM SAID SOLUTION AT SAID TEMPERATURE, SAID TRIPLE SALT FIELD HAVING THE SHAPE OF AN IRREGULAR PENTAGON WHOSE CORNERS A, B, C, D AND E, RESPECTIVELY, HAVE THE POSITIONS ON SAID PHASE DIAGRAM DEFINED BY THE FOLLOWING EQUATIONS: 